A communication system can be seen as a facility that enables communication between two or more entities such as user equipment and/or other nodes associated with the system. A communication system typically operates in accordance with a given standard or specification which sets out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely the user equipment or terminal, is provided with a packet switch server and/or a circuit switch server. Communication protocol and/or parameters which are used for the connection may also be defined. In other words, a specific set of “rules” on which the communication can be based need to be defined to enable communication by means of the system.
Communication systems providing wireless communication for the user terminal or other nodes are known. An example of a wireless system is a cellular network. In cellular systems, a base transceiver station (BTS) or similar access entity serves mobile stations (MS) or similar wireless user equipment (UE) via a wireless interface between these entities. The operation of the base station and other nodes required for the communication can be controlled by one or several control entities. The various control entities may be interconnected. One or more gateway nodes may also be provided for connecting the cellular network to other networks such as to a public switched telephone network (PSTN) and/or other communication networks such as an IP (internet protocol) and/or other packet switched networks.
A communication system may be adapted to provide wireless data communication services such as packet switched (PS) services for a mobile station. Examples of systems enabling wireless data communication services, without limitation to these, include the general packet radio service (GPRS), the enhanced data rate for GSM evolution (EDGE) mobile data network, the so-called third generation (3G) telecommunication systems such as the universal mobile telecommunication system (UMTS), i-phone or IMT-2000 (international mobile telecommunications) and the terrestrial trunked radio (TETRA) system.
In the third generation system, it has been proposed to provide a multimedia network architecture. It is intended that a multimedia architecture be able to handle different kinds of data such as voice, audio, video, data per se and indeed any other type of media. It has been proposed to have an IP (internet protocol) multimedia subsystem for such a network architecture. Thus, the subsystem of the architecture is arranged to transfer data between the various entities in packet data form, in accordance with the internet protocol.
The IP multimedia subsystem comprises all core network elements for provision of a multimedia service. This includes the collection of signalling and bearer related network elements. IP multimedia services are arranged to use the packet switch domain. The IP multimedia core network is arranged to enable PLMN operators to offer their subscribers multimedia services based on and built upon internet applications, services and protocols. It is intended that the IP multimedia core network subsystem should enable convergence of and access to voice, video, messaging, data and web based technology for wireless users.
The proposed third generation multimedia network architecture may have several different servers for handling different functions. These include functions such as the call state control functions (CSCFs). The call state control function may comprise functions such as a proxy call state control function (P-CSCF), interrogating call state control function (I-CSCF), and serving call state control function (S-CSCF). Control functions may also be provided by entities such as a home subscriber server (HSS) and various application servers.
In the currently proposed specification, Third Generation Partnership Project; Technical Specification Group Services and System Aspect; IP multimedia subsystem (IMS) stage 2, (release 5), which is herein incorporated by reference, there are various identities that may be associated with a user of an IP multimedia service. These identities include private user identity and public user identities. These identities are provided in an IM Subscribers Identity Module ISIM. Each ISIM is an application in the Universal Integrated Circuit Card UICC card of the user equipment. However, in earlier versions of the specification, the UMTS Subscriber Identity Module USIM application in the UICC card did not include these additional identities. UICC card which conforms to the previous versions of this standard (R99 or Rel-4) can be sold or owned by the subscriber. However, if a user of equipment which is in accordance with the Rel-5 version of the specification were to try to use an IP multimedia system, they would be unable to do so.
It has been suggested that the required IP multimedia subsystem identities be derived directly from the international mobile subscriber identifier (IMSI). However, this has the disadvantage in that this leads to security and optimisation problems. Additionally, the public user identities are not user friendly as john.smith@vodafone.com. Rather a public user identity derived from the IMSI would be something like 336574890@22081). Furthermore, additional data base searches would need to be carried out in order to check if the derived public and private user identities were valid.